1. Field of the Invention
The present invention relates to a sensor equipped wheel support bearing assembly having a load sensor built therein for detecting a load that acts on a bearing unit rotatably supporting a vehicle wheel.
2. Description of the Prior Art
For safety travel of an automotive vehicle, a wheel support bearing assembly equipped with a sensor for detecting the rotational speed of each of vehicle wheels has hitherto been well known in the art. While the automobile traveling safety precaution is generally taken by detecting the rotational speed of the respective vehicle wheel in various locations, it is not sufficient with only the rotational speed of the vehicle wheel and, therefore, it is desired to achieve a control with the use of other sensor signals for safety purpose.
In view of the above, it may be contemplated to achieve the vehicle stability control based on a load acting on each of the vehicle wheels during travel of an automotive vehicle. By way of example, a large load acts on the outside wheels during the cornering, on the wheels on one side during the run along horizontally inclined road surfaces, or on the front wheels during braking, and thus, a varying load acts on the vehicle wheels. Also, even in the case of the uneven live load, the loads acting on the respective wheels tend to become uneven. For this reason, if the loads acting on the wheels can be detected as needed, suspension systems for the vehicle wheels can be controlled beforehand based on results of detection of the loads so that the stability control of the automotive vehicle during the traveling thereof (for example, prevention of a rolling motion during the cornering, prevention of sinking of the front wheels during braking, and prevention of sinking of the vehicle wheels brought about by an uneven distribution of live loads) can be accomplished. However, an appropriate space for installation of the load sensor for detecting the load acting on the respective vehicle wheel can hardly be found and, therefore, the vehicle stability control through the detection of the load is difficult to realize.
Also, in the event in the near future a steer-by-wire is introduced and the system, in which the wheel axle and the steering come not to be coupled mechanically with each other, is increasingly used, transmission of information on the road surface to the steering wheel hold by a driver, by detecting a wheel axis direction load would come to be required.
In order to meet those needs hitherto recognized, a wheel support bearing assembly has been suggested, in which a strain gauge is affixed to an outer ring of the wheel support bearing assembly for the purpose of detecting strains. (See, for example, the Patent Document 1 listed below.)    [Patent Document 1] Japanese Laid-open Patent Publication No. 2003-530565
Since the outer ring of a wheel support bearing assembly is a bearing component part having a rolling surface defined therein and required to have a strength, which bearing component part is manufactured through complex process steps including, for example, a plastic working, a turning process, a heat treatment and a grinding process, there is a problem in that the productivity is low and the cost of manufacture thereof during a mass production tends to become high where a strain gauge is attached to the outer ring such as disclosed in the Patent Document 1 referred to above. Also, it is not easy to detect a strain occurring in the outer ring with high sensitivity and, when a result of such detection is utilized in controlling the vehicle stability of an automotive vehicle then travelling, a problem will arise in association with the accuracy of the control.
In view of the foregoing, attempts have been made to secure a strain generating member to an outer member and then to fit a sensor element for the measurement of strains to such strain generating member. When this construction is employed, it is sufficient to fix the strain generating member with the sensor element fitted thereto, to the outer ring and, therefore, the productivity can be increased. However, detection of the strains occurring in the outer ring with high sensitivity is still not satisfactory.